What's the problem this feature will solve?

The documentation for caplog.set_level() says

Set the level of a logger for the duration of a test.

This does not make it clear that it's setting the threshold level for capturing logging.

Describe the solution you'd like

The Python logging documentation makes this clear for logging.setLevel():

Sets the threshold for this logger to level. Logging messages which are less severe than level will be ignored; ...

caplog.set_level() ought to do the same.

Additional context

The only reason I know it's a threshold is because I tried running pytest -rA with different levels set in caplog and the output contained messages at that level and above